Formation of integrated circuits requires that a metal substance be placed in contact with the active area of the integrated circuits so that the integrated circuit device may be connected to other such devices, or so that the integrated circuit may be connected to other components of an electromechanical system. It is generally desirable to use a metal material which is highly conductive. To this end, it is desirable to use copper.
Although the use of copper in an integrated circuit metallization process has some problems, it is desirable to use CVD copper as a high-performance metal film to replace aluminum and its alloys, which are currently the most commonly used metallization substances in integrated circuit construction. One of the most significant difficulties encountered with using copper for metallization has been the poor adhesion exhibited by copper when deposited by CVD. In some instances, a sputtered copper film has been laid down as a seed layer prior to the deposition of copper by CVD. N. Awaya et aL, Evaluation of Copper Metallization Process And The Electrical Characteristics Of Copper Interconnected Quarter-Micron CMOS, IEEE Trans. Electron Dev. 43 (1996) p.1206. This appears to promote adhesion of the copper to the underlying silicon-based structures. This is believed to occur because the sputtered copper is virtually pure copper and is deposited at a high kinetic energy, and forms a molecularly uniform layer of metal which forms a stronger bond with the underlying structure and which, therefore, exhibits better adhesion properties. The sputtering process, however, is costly, both in terms of time and equipment, and results in metal coverage in trenches and holes which is of poor quality.
Metal organic CVD has also been used to deposit a more uniform metal layer, as has providing some type of adhesion promoter on the substrate before the metallization step. For a variety of reasons, these procedures do not work well, with the main problem being that the copper separates from the underlying substrate.